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A spate of recent coronavirus infections among vaccinated athletes and officials has drawn attention to an apparent increase in so-called “breakthrough” infections. But as cases involving fully vaccinated people have increased in recent weeks, experts say there is little cause for concern.
A game between the New York Yankees and the Boston Red Sox on July 15 has been postponed due to several confirmed cases of the breakthrough. Days later, Kara Eaker, a replacement for the U.S. women’s gymnastics team who was vaccinated in May, tested positive at an Olympic Games training camp in Japan. And this week, government officials announced that a White House staff member and senior communications assistant to House Speaker Nancy Pelosi, D-Calif., Had tested positive even though they had been fully vaccinated. The cases arose after six members of a Texas Democrat delegation tested positive in Washington, DC
Comprehensive coverage of the Covid-19 pandemic
More than 161 million people in the United States have been fully vaccinated, according to the Centers for Disease Control and Prevention, and groundbreaking infections appear to only occur in a tiny fraction of them.
But as the pandemic persists and more transmissible variants of the virus circulate widely, the number of breakthrough infections is expected to increase. Yet studies have shown that most cases in people vaccinated are mild – if a person develops symptoms – and research indicates that vaccines still offer strong protection, even against known variants.
“The reality is that a lot of these breakthrough infections have been from vaccinated people who test positive, but there is a difference between testing positive and getting sick,” said Angela Rasmussen, virologist at the Vaccine and Infectious Disease Organization at the University of Saskatchewan in Canada.
In other words, people who test positive may have tiny amounts of the virus in their bodies – enough to be detected with Covid-19 tests but not enough to make them sick.
And because vaccines work by stimulating the immune system, it can recognize and attack any invading pathogen faster.
“If you have a lot of good antibodies, they are potentially able to bind to the virus before it causes problems, and this may lessen or decrease your chances of getting sick,” said Dr. Robert Darnell, senior physician and biochemist at Rockefeller University in New York.
Yet revolutionary infections are expected because no vaccine is 100 percent effective. In rare cases, fully vaccinated people can become seriously ill and die from Covid-19, but the vast majority of groundbreaking cases have been mild or asymptomatic.
This is because vaccines act like screens to keep most, but not necessarily all, viral particles from entering the body. Different factors influence the strength of the screen and the number of tiny viral particles able to cross the barrier, said Dr. Sarah Fortune, an immunologist at the TH Chan School of Public Health at Harvard.
“These variants are more transmissible, so they pass through screens better,” she said. “The other factor is how much virus is trying to get in, and that’s determined by the vaccination rates in your local community. It’s how much virus you’re exposed to.”
Vaccines can also reduce the amount of the virus in the body, which may limit the ability of people with chronic infections to pass it on to others, although the effect is not yet fully understood. More research is needed to assess the effect of cases of asymptomatic breakthrough, in particular, on transmission.
“It may be that for the vast majority of vaccinated people who are infected, they simply do not produce enough virus to infect another person,” said Dr Janko Nikolich-Žugich, immunologist and professor of medicine at the University. from Arizona.
Darnell, of Rockefeller University, said the recent increase in breakthrough infections has not been associated with a similar increase in hospitalizations or deaths, which is encouraging evidence that the vaccines appear to be holding up well, despite the newer variants. and emerging.
The CDC initially tracked all cases of breakthrough infections, but from May 1 it shifted to focusing only on cases related to hospitalization or death. By that time, more than 100 million people in the United States had been fully vaccinated, and the CDC had documented more than 10,000 cases of major infections.
As of July 12, the CDC has reported 5,492 breakthrough cases in which patients have been hospitalized or have died. Three quarters of the cases involved people over 65. Although they are classified as breakthrough infections, it is not necessarily the case that Covid-19 has caused hospitalizations or deaths, especially in asymptomatic patients.
Rasmussen said the higher rates of hospitalization and death among the elderly are not surprising because the elderly are generally more vulnerable to serious illnesses from Covid-19. People who are immunocompromised or those with underlying illnesses are also at greater risk.
In Israel, where 80 percent of people 16 and older have been fully vaccinated, researchers looked at 152 groundbreaking cases in which patients were hospitalized and found most of them were people with underlying conditions, such as hypertension, diabetes and congestive heart failure. The study, published July 6 in the journal Clinical Microbiology and Infection, found that only six cases involved patients without comorbidity.
Israel reported this month that the Pfizer-BioNTech vaccine was 93% effective in preventing hospitalizations and serious illness, but its effectiveness fell to 64% in preventing infections and symptomatic illnesses.
A separate analysis published on June 25 by Public Health England found that two injections of the Pfizer-BioNTech and AstraZeneca vaccines were 79% effective in protecting against symptomatic illness with the delta variant and 96% effective against hospitalization.
The ability of vaccines to protect against serious illness is critical, Rasmussen said, and says injections continue to work well.
“If we started to see intensive care units filling up with fully vaccinated people, that would indicate that the vaccines are no longer effective,” she said.
Although the vaccines remain very effective, there is cause for concern if epidemics continue to smolder across the country. The more the virus is allowed to circulate, the more likely the pathogen is to mutate in a way that could make it more transmissible, allow it to cause more serious disease, or help it escape the protection of vaccines.
“Every pathogen arms race ends badly because it’s fundamentally an evolution,” Fortune said. “What we’re talking about is that the virus is trying not to die out, and evolution is going to promote transmission. Evolution is going to promote vaccine escape.”
Preventing such an outcome will require focusing on vaccinating as many people as possible, in the United States and around the world.
“I am losing infinitely more sleep because of the fact that we have such a large number of unvaccinated people who are at enormous risk of developing serious illness,” Nikolich-Žugich said. “We shouldn’t be complacent or cavalier about this, but it pales in comparison to the question of how to get as many people vaccinated as possible.”
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